1. Field of the Invention
The invention relates to x-ray installations and, more particularly in an installation of this type, to an x-ray equipment stand which permits isocentric scanning or examination of a patient at multiple angles of incidence.
2. Description of the Prior Art
X-ray examination of a patient is performed by means of an imaging chain which, as a general rule, is essentially constituted by an x-ray source, a collimator, an anti-diffusion grid and a receiver which are carried in rigidly assembled relation by a structure known as a stand.
The x-ray source and the collimator are located on the same side with respect to the patient to be examined who is placed on a table whilst the anti-diffusion grid and the receiver are on the opposite side. A straight line passing through the focus of the x-ray source and the center of the receiver represents the axis of x-radiation or imaging chain axis. In the case of isocentric scanning or examination, this axis always passes through the same point of a zone to be scanned irrespective of the orientation of said axis and this point constitutes the isocenter. The movement which makes it possible to vary the orientation of the imaging chain axis with respect to the isocenter is known as an isocentric movement.
Stands which serve to carry out an isocentric movement usually consist of an open arch or arcuate member, one end of which carries the x-ray source and the other end of which carries the receiver. The axis of the imaging chain passes through the isocenter which constitutes the center of the arcuate member or is located on the same axis as the center of the arcuate member so that a first isocentric movement is performed by rotating the arcuate member about its center in its plane, for example by displacing the arcuate member in sliding motion within a sleeve having the shape of a circular arc.
X-ray equipment stands permit in addition a second isocentric movement which consists of rotation of the plane of the arcuate member about a second axis of rotation which is perpendicular to the first and also passes through the isocenter.
In certain x-ray equipment stands, provision is made for a third isocentric movement which consists of a rotation about a third axis of rotation which is perpendicular to the plane of the first and second axes and passes through the isocenter.
It is apparent that these three isocentric movements make it possible to take pictures of the patient in incidence and in planes which can be oriented in all directions in space.
In an x-ray installation, the patient is placed on a table which permits displacements of the patient in three directions, namely one direction in elevation (z-axis) and two directions in the horizontal plane (x-axis in the longitudinal direction of the patient and y-axis in the perpendicular direction). The aim of these movements is to cause the isocenter to coincide with the center of the zone to be examined.
An installation of this type is attended by a certain number of disadvantages. One disadvantage lies in the fact that it is cumbersome since it calls for the use of a patient support table which moves in the horizontal plane so as to place the center of the zone to be observed at the isocenter of the stand.
Another disadvantage is that the stand has considerable overhang since it has to permit longitudinal displacement of the patient over a substantial width. This also has the effect of increasing the bulk of the installation.